Many of users do not use powerful Maxima computer algebra system for systematic work, but for ad hoc algebraic calculations – equations, functions, matrixes, etc. only.
To do this job, it is not useful to download the whole application from a web site.

diff (<expr>, <x>) returns the first derivative of <expr> with respect to the variable <x>.

diff (<expr>) returns the total differential of <expr>, that is, the sum of the derivatives of <expr> with respect to each its variables times the differential del of each variable. No further simplification of del is offered.

The noun form of diff is required in some contexts, such as stating a differential equation. In these cases, diff may be quoted (as diff) to yield the noun form instead of carrying out the differentiation.

When derivabbrev is true, derivatives are displayed as subscripts. Otherwise, derivatives are displayed in the Leibniz notation, dy/dx.

For the tensor package, the following modifications have been incorporated:

(1) The derivatives of any indexed objects in <expr> will have the variables <x_i> appended as additional arguments. Then all the derivative indices will be sorted.

(2) The <x_i> may be integers from 1 up to the value of the variable dimension [default value: 4]. This will cause the differentiation to be carried out with respect to the <x_i>th member of the list coordinates which should be set to a list of the names of the coordinates, e.g., [x, y, z, t]. If coordinates is bound to an atomic variable, then that variable subscripted by <x_i> will be used for the variable of differentiation. This permits an array of coordinate names or subscripted names like X[1], X[2], ... to be used. If coordinates has not been assigned a value, then the variables will be treated as in (1) above.

There are also some inexact matches for diff. Try ?? diff to see them.